Method and apparatus for detecting imminent structural failure of an electrical lead in an implanted cardiac therapy medical device

• US 20100318141A1
• Filed: 12/11/2009
• Published: 12/16/2010
• Est. Priority Date: 06/15/2009
• Status: Active Grant

• Current Assignee: Kallis Technical Services
• Original Assignee: Kallis Technical Services
• Inventors: Kallis, James M.
• Granted Patent: US 8,406,892 B2
• Time in Patent Office: Days
• US Class Current: 607/5
• CPC Class Codes: A61N 1/3706 Pacemaker parameters stimulation threshold A61N1/371
• CPC Class Codes: A61N 1/371 Capture, i.e. successful stimulation
• CPC Class Codes: A61N 2001/083 Monitoring integrity of contacts, e.g. by impedance measurement

Abstract

A method and apparatus implementing the method, which is not dependent on monitoring the electrical impedance of the lead, detects imminent structural failure of an electrical lead in an implanted medical device, such as an implantable cardioverter-defibrillator (ICD) or a pacemaker. The approach is to monitor directly the mechanical load loss of the lead (a measure of the loss of structural integrity of the lead) rather than, as in the prior art, to infer it from the electrical impedance.

Claims

1. In a cardiac therapy medical device implanted in a patient wherein the medical device has electrical leads subject to structural failure, a method for detecting imminent structural failure of any of the electrical leads in the implanted medical device comprising the step of directly monitoring any loss of structural integrity of the electrical leads.

2. The method according to claim 1 in which said monitoring step includes the step of monitoring the mechanical load loss of any of the electrical leads.

3. The method according to claim 1 in which said monitoring step comprises the step of monitoring directly the mechanical load loss of the lead as detected in any decrease in the mechanical load required to deflect and/or elongate the electrical leads by a specified amount.

4. The method according to claim 1 in which said monitoring step includes the step of detecting any deflection and/or elongation of the electrical leads resulting from movement of the patient.

5. The method according to claim 1 in which said monitoring step comprises the step of detecting the decrease in the mechanical load required to deflect or elongate the electrical leads by a specified amount.

6. The method according to claim 1 in which said monitoring step comprises the step of measuring the mechanical load on the electrical leads versus deflection of the lead as a function of time after implantation.

7. The method according to claim 4 wherein the medical device comprises an implantable cardioverter-defibrillator.

8. The method according to claim 4 wherein the medical device comprises a pacemaker.

9. For use with a medical device to be implanted in a patient, a method for detecting lead failure in the implanted medical device comprising the steps of:

(a) deriving an empirical formula by

(i) selecting samples of cardiac therapy medical device leads of the model number of the medical device from the production line;

(ii) subjecting the leads to destructive laboratory pull testing by

(α

) pulling the leads and measuring the elongation (E) and the baseline mechanical load (L_B) of the leads,

(β

) growing flaws in the leads,

(γ

) again pulling the flawed leads and measuring the elongation (E) and the baseline mechanical load (L_B) of the flawed leads, thereby obtaining test results,

(iii) based upon the test results, evaluating the threshold mechanical load (L_T) and the threshold mechanical load loss (Δ

L_T=L_B−

L_T) as a function of the elongation (E),

(iv) fitting the threshold test data to an empirical formula of the general form Δ

L_T=f_T(E) to determine the best-fit function and the best-fit parameters,

(v) storing the empirical formula in the cardiac therapy medical device computer;

(b) for each serial number of a lead in an implanted device,

(i) establishing a baseline immediately after the lead is installed into the cardiac therapy medical device during fabrication of the device,

(ii) subjecting the installed lead to a nondestructive laboratory pull test,

(iii) measuring the elongation (E) and the baseline mechanical load (L_B),

(iv) fitting the baseline test data to a formula L_B=f_B(E),

(v) determining the best-fit function and the best-fit parameters,

(vi) storing the empirical formula in the serial number of the cardiac therapy medical device computer,

(c) implanting the cardiac therapy medical device in the patient;

(d) operating the cardiac therapy medical device to continuously monitor the cardiac therapy medical device computer to monitor any elongation of the lead resulting from patient movements,

(i) when any elongation is sensed, measuring the elongation (E) and any corresponding mechanical load (L),

(ii) determining by use of the cardiac therapy medical device computer whether the threshold for imminent structural failure has been reached by comparing the mechanical load loss (Δ

L=L_B(E)−

L) with the threshold mechanical load loss (Δ

L_T(E)),

(iii) should Δ

L≧

Δ

L_T(E), that is, if L≦

f_B(E)−

f_T(E), alerting the patient by use of the cardiac therapy medical device computer that structural failure of the lead is imminent,

(iv) should Δ

L<

Δ

L_T(E), that is, if L>

f_B(E)−

f_T(E), continuing operation of the cardiac therapy medical device.

10. For use with a medical device to be implanted in a patient, a method for detecting failure of a lead in the implanted medical device comprising the operational steps of:

operating the medical device to continuously monitor a medical device computer for monitoring any elongation of the lead resulting from patient movements,

when any elongation is sensed, measuring the elongation (E) and any corresponding mechanical load (L),

determining by use of the computer whether the threshold for imminent structural failure has been reached by comparing the mechanical load loss (Δ

L=L_B(E)−

L) with the threshold mechanical load loss (Δ

L_T(E)),

should Δ

L≧

Δ

L_T(E), that is, if L≦

f_B(E)−

f_T(E), alerting the patient by use of the computer that structural failure of the lead is imminent, and

should Δ

L<

Δ

L_T(E), that is, if L>

f_B(E)−

f_T(E), continuing operation of the medical device.

11. The method according to claim 10, comprising the pre-operational steps comprising the steps of:

deriving an empirical formula by

(i) selecting samples of leads of the model number of the medical device from the production line;

(ii) subjecting the leads to destructive laboratory pull testing by measuring the elongation (E) and the baseline mechanical load (L_B) of the leads under varying conditions of the leads to obtain relative test results,

(iii) based upon the test results, evaluating the threshold mechanical load (L_T) and the threshold mechanical load loss (Δ

L_T=L_B−

L_T) as a function of the elongation (E),

(iv) fitting the threshold test data to an empirical formula of the general form Δ

L_T=f_T(E) to determine the best-fit function and the best-fit parameters,

(v) storing the empirical formula in the computer;

for each serial number of a lead in an implanted device,

(i) establishing a baseline immediately after the lead is installed into the cardiac therapy medical device during fabrication of the device,

(ii) subjecting the installed lead to a nondestructive laboratory pull test,

(iii) measuring the elongation (E) and the baseline mechanical load (L_B),

(iv) fitting the baseline test data to a formula L_B=f_B(E),

(v) determining the best-fit function and the best-fit parameters, and

(vi) storing the empirical formula in the serial number of the computer.

12. A cardiac therapy medical device implanted in a patient wherein the medical device has at least one electrical lead subject to structural failure, a monitor for detecting imminent structural failure of the electrical lead in the implanted medical device comprising measuring apparatus coupled to the electrical lead and the medical device for directly monitoring any loss of structural integrity of the electrical leads.

13. The device according to claim 12 in which said measuring apparatus includes a mechanism for measuring the mechanical load loss of the electrical lead.

14. The device according to claim 12 in which said measuring apparatus comprises a mechanism for directly measuring the mechanical load loss of the lead as detected in any decrease in the mechanical load required to deflect and/or elongate the electrical lead by a specified amount.

15. The device according to claim 12 in which said measuring apparatus includes a mechanism for detecting any deflection and/or elongation of the electrical lead resulting from movement of the patient.

16. The device according to claim 12 in which said measuring apparatus comprises a mechanism for detecting any decrease in the mechanical load required to deflect or elongate the electrical lead by a specified amount.

17. The device according to claim 13 in which said mechanism includes implementation for measuring the loss of structural integrity of the electrical lead.

18. The device according to claim 12 in which said mechanism includes implementation for measuring the mechanical load on the electrical lead versus deflection of the lead as a function of time after implantation.

19. The device according to claim 12 wherein the medical device comprises an implantable cardioverter-defibrillator.

20. The device according to claim 12 wherein the medical device comprises a pacemaker.